Structures for supplying RF energy to subsurface formations have been proposed such as those disclosed in U.S. Pat. No. 4,140,179 wherein a coaxial line extending through an outer casing terminates in a dipole arrangement in a body of oil shale. However, in such structures, portions of the energy were lost due to RF currents flowing back up the bore hole on the outside of the coaxial line. Thus, the heating of the subsurface body occurred partly above the region where the heating was desired. The dipole arrangement was such that the impedance match to the coaxial line and the radiation pattern were very sensitive to changes in the impedance of the shale due to changes in temperature and content of organic material.